New Avialan Remains and a Review of the Known Avifauna from the Late Cretaceous Nemegt Formation of Mongolia

2004·0.43 MB·English

by  Julia A. Clarke

PUBLISHED BY THE AMERICAN MUSEUM OF NATURAL HISTORY
CENTRAL PARK WEST AT 79TH STREET, NEW YORK, NY 10024
Number 3447, 12 pp., 3 figures, 2 tables June 2, 2004
New Avialan Remains and a Review of the
Known Avifauna from the Late Cretaceous
Nemegt Formation of Mongolia
JULIA A. CLARKE1 AND MARK A. NORELL2
ABSTRACT
Small vertebrates have remained relatively poorly known from the Nemegt Formation, al-
though it has produced abundant and well-preserved large dinosaur remains. Here we report
three new avialan specimens from the Late Cretaceous (Maastrichtian) of Omnogov Aimag,
Mongolia. These fossils were collected from the Nemegt Formation exposedatthelocalityof
Tsaagan Khushu in the southern Gobi Desert. All of the new finds are partial isolated bones
with a limited number of preserved morphologies; however, they further understanding of
dinosaur diversity in the Late Cretaceous of Mongolia and, specifically, from the Nemegt
Formation. The new specimens are described and evaluated in phylogenetic analyses. These
analyses indicate that all three fossils are placed as part of the clade Ornithurae.
Avialan diversity of the Nemegt Formation is reviewed and briefly compared with that of
the underlying Djadokhta and Barun Goyot Formations. These formations have been consid-
eredtorepresentatleasttwodistinctLateCretaceousenvironments,withtheNemegttypically
interpreted as representing more humid conditions. Ornithurine and enantiornithine birds are
known from the Nemegt as well as the Djadokhta and Barun Goyot Formations, although
ornithurine remains are more common in the Nemegt. No avialan species known from the
Djadokhta, or Barun Goyot, are also known from the Nemegt Formation and, overall, the
avialan taxa from these formations do not appear more closely related to each other than to
other avialans. Whether these faunal differences are best interpreted as environmental, tem-
poral, or sampling/preservational should be further investigated.
1Division of Paleontology, American Museum of Natural History; North Carolina State University and North
CarolinaMuseumofNaturalSciences(Julia(cid:112)[email protected]).
2DivisionofPaleontology,AmericanMuseumofNaturalHistory([email protected]).
Copyright(cid:113)AmericanMuseumofNaturalHistory2004 ISSN0003-0082
2 AMERICAN MUSEUM NOVITATES NO. 3447
Fig.1. MapofMongoliaindicatingwherethefossilswererecovered,thelocalityofTsaaganKhushu
in the western Gobi Desert (Omongov Aimag).
INTRODUCTION lected in 2001. None of the specimens ap-
pears to be from a juvenile animal;muscular
Three new avialan fossils were collected
scars and tubercles are well developed, the
from the Maastrichtian (Martinson et al.,
bone surfaces are smooth, and the proximal
1969) Nemegt Formation (Efremov, 1954;
tarsals are completely fused to the tibia in
but see Gradzinski et al., 1977) in southern
IGM 100/1310.
Mongolia by the Mongolian Academy of
The Nemegt Formation has been inter-
Sciences/American Museum of Natural His-
preted as representing a dominantly fluvial
tory (MAS/AMNH) expeditions in 2000 and
environment with most fossils from channel
2001. The finds are all partial,isolatedbones
fill, point bar, and occasional overbank de-
recovered from the western exposures of
Tsaagan Khushu (Gradzinski et al., 1977), a posits laid down under more humid condi-
locality in the Nemegt Basin (Omongov tions than in the underlying Djadokhta For-
Aimag, Mongolia; fig. 1). All three speci- mation (Gradzinski, 1970; Jerzykiewicz and
menswerefoundindistinct,small,well-sort- Russell, 1991). In marked contrast to the un-
ed sand lenses comparatively rich in isolated derlying DjadokhtaFormation(Dashzeveget
small vertebrate elements (e.g., fish verte- al., 1995), the remains of small vertebrates
brae, turtle plastron, and carapace frag- are rare from the Nemegt Formation, which
ments). A proximal tibiotarsus (IGM 100/ has produced abundant and well-preserved
1311) described here was discovered during large dinosaur remains (Osmo´lska, 1980;
the2000MAS/AMNHexpedition,andadis- Barsbold, 1983). The Nemegt fauna has also
tal tibiotarsus (IGM 100/1310) as well as a been described as more cosmopolitan than
proximalhumerus(IGM100/1309)werecol- that of the Djadokhta, having stronger affin-
2004 CLARKE AND NORELL: NEW AVIALAN FOSSILS FROM MONGOLIA 3
ities to faunas from North American Late AmericanMuseumofNaturalHistory;IGM,
Cretaceous localities (Jerzykiewicz and Rus- InstituteofGeology,MongolianAcademyof
sell, 1991). Sciences, Ulaanbaatar.
Previously describedavialanremainsfrom
the Nemegt Formation include five isolated DESCRIPTION OF THE NEW
and incomplete bones referred to the Hes- MATERIAL
perornithes (Kurochkin, 2000) and two spec-
imens comprising associated forelimb ele- IGM 100/1309 is a proximal left humerus
ments that are the holotypes of the enantior- (fig. 2A; table 1). The humeral head is glo-
nithine Gurilynia nessovi (Kurochkin, 1999) bose but comparatively weakly expanded
and proposed presbyornithid anseriformTev- proximally and anteroposteriorly. The pneu-
iornis gobiensis (Kurochkin et al., 2002). motricipital fossa is comparatively diminu-
The small theropod Mononykus olecranus tive, does not excavate the distal surface of
(Perle et al., 1993) was also described from theventraltubercle,anddoesnotcontainany
the Nemegt Formation (at Bugin Tsav) as a pneumatic foramina. The dorsal surface of
basal avialan (Perle et al., 1993); however, the ventral tubercle bears a depressed, sub-
this taxon and other alvarezsaurids are now triangular scar. The bar that demarcates the
most often placed phylogenetically outside dorsal edge of this fossa in Aves (crus dor-
Avialae (e.g., Norell et al., 2001). The exis- sale; Baumel and Witmer, 1993) is essential-
tence of specimens of ‘‘graculavid charadri- ly absent. At the dorsal edge of the pneu-
iforms’’ or ‘‘transitional shorebirds’’, and motricipital fossa is a slight ridge, or raised
crown clade avian taxa including presbyor- intermuscular scar. A concavity lying just
nithid anseriforms, phalacrocoracids, and di- dorsal to this ridge (fig. 2A) may correspond
omediids, in the Nemegt Formation has also to a feature identified as the m. scapulohu-
been indicated (Kurochkin, 2000: 556). meralis cranialis attachment in Presbyornis
However, so far only one of these specimens pervetus (Ericson, 1999) that is also present
has been described (Kurochkin et al., 2002) in the presbyornithid Telmabates antiquus
and one isolated tarsometatarsus from the holotype (AMNH 3170). In IGM 100/1309,
Barun Goyot Formation (Kurochkin, 2000) this scar is not bounded dorsally, while in
was recently removed from the Presbyorni- Presbyornis pervetus and Telmabates antiq-
thidae (Kurochkin et al., 2002). Thus, with uus this scar is bounded by a continuationof
the exception of the large enantiornithine the dorsal edge (crus dorsale; Baumel and
Gurilynia nessovi, all of the avialan taxa Witmer, 1993) of the pneumotricipital fossa.
from the Nemegt have been considered parts A second fossa (fig. 2A) strongly under-
of Ornithurae, either as relatively closely re- cuts the posterodistal edge of the humeral
lated to Aves as part ofHesperornithes,oras head and is open to the capital incisure de-
parts of crown clade avian lineages. veloped between the head and the well-pro-
The taxonomic status of previously dis- jected ventral tubercle. Just dorsal to the hu-
coveredavialanfossilsfromtheNemegtFor- meral head, a scar-marked dorsal tubercle is
mation is briefly reviewed here, and known visible (fig. 2A). From the preserved frag-
Nemegt avialan diversity is compared tothat ment of the deltopectoral crest it cannot be
from the underlying Djadokhta and Barun determined whether it was deflected anteri-
Goyot Formations. Gradzinski et al. (1977) orly or dorsally. The proximoposterior sur-
suggested, on the basis of faunal differences, face of the crest is concave. The lig. acro-
thattheBarunGoyotFormationwasyounger coracohumeraleattachmentisdevelopedasa
than the Djadokhta Formation. However, discrete fossa, rather than as a transverse
morerecentworkhasnotsupportedthiscon- groove.
clusion, instead implying that the Djadokhta IGM 100/1310 is a slightly abraded prox-
and Barun Goyot are nearly coeval (Jerzyk- imal left tibiotarsus from an avialan approx-
iewicz and Russell, 1991; Dashzeveg et al., imately the size of Gallus gallus (fig. 2B;
1995;Jerzykiewiczetal.,1993;GaoandNo- table 1). Both anterior and lateral cnemial
rell, 2000). crests are clearly developed. Although the
INSTITUTIONAL ABBREVIATIONS: AMNH, midsection of the patellar crest and antero-
4 AMERICAN MUSEUM NOVITATES NO. 3447
Fig. 2. A. IGM 100/1309 in (left) posterior, (middle) anterior, and (right) proximal views. B. IGM
100/1310 in (left) anterolateral, (middle) medial, and (right) proximalviews. C. IGM100/1311in(left)
anterior, (middle) posterior, and (right) distal views. Anatomical abbreviations: acm, anterior cnemial
crest; cap, capital incisure; dep, depression (m. scapulohumeralis cranialis attachment?); dt, dorsal
2004 CLARKE AND NORELL: NEW AVIALAN FOSSILS FROM MONGOLIA 5
TABLE1 PHYLOGENETIC ANALYSES
Measurementsof NewMongolianFossils(mm)
To assess the phylogeneticrelationshipsof
the new specimens, they were scored for
characters in the Clarke and Norell (2002)
matrix, which includes 185 characters infor-
mative for the 15 ingroup and two outgroup
taxa.ThisdatasetwasanalyzedusingPAUP*
4.0b8[PPC] (Swofford, 2001). The three
specimens (IGM 100/1309, IGM 100/1310,
and IGM 100/1311) were included as sepa-
rate terminals since they were unassociated,
and there is no evidence that they represent
a single taxon. Analysis settings were the
same as those in Clarke and Norell (2002):
all searches were branch and bound; ‘‘amb’’
in the ‘‘Parsimony Settings’’ menu was se-
lectedsuchthatinternalbrancheswithamin-
imum length of 0 were collapsed to form a
proximalportionoftheanteriorcnemialcrest soft polytomy; and ambiguity was distin-
are abraded, it can be determined from their guished from polymorphism. The scorings
intact portions that neither cnemial crestwas for the new Mongolian specimens are given
well projected proximally. The medial con- in appendix 1.
dyle is large and flat, while the lateral is Inclusion of the three terminals IGM 100/
strongly convex. A tuberculated scar (fig. 1309, IGM 100/1310, and IGM 100/1311
2B) is projected medially from the midpoint yielded 316 most parsimonious trees(MPTs)
of the medial edge of the tibiotarsus in prox- 392 steps in length. A strict consensus of
imal view. these topologies (fig. 3) places the three new
IGM 100/1311 is a distal right tibiotarsus elements in a polytomy including Apsaravis
missing most of its medial condyle (fig. 2C; ukhaana and all taxa more closely related to
table 1). The extensor groove is broad and crowncladeAvesthanthattaxon.Thus,they
well developed but is not covered distallyby are all found to be part of Ornithurae (sensu
an osseous bridge. The extensor retinaculum Gauthier and de Queiroz, 2001; see also dis-
tubercles are developed, and the fibular cussion in Clarke and Norell, 2002 and
grooveisdeeplyimpressedandboundedme- Clarkeetal.,2002).Therestoftherecovered
dially by a pronounced ridge(fig. 2C).There topology is the same as that in Clarke and
is a slight medial deflection and mediolateral Norell (2002)totheextentthatitisresolved.
widening of the distalmost tibia. The shaftis The Mongolian specimens were then in-
compressed anteroposteriorly. Posteriorly, cluded individually into further phylogenetic
thesurfaceforarticulationwiththetibialcar- analyses. The analysisincludingonlythehu-
tilage (i.e., trochlea cartilaginis tibialis;Bau- merus (IGM 100/1309) of the three speci-
meland Witmer,1993)extendsjustproximal mens produced 2 MPTs also of 392 steps.
to the level of the condyles (fig. 2C, center). Thesetwotreesdifferonlyinenantiornithine
Themedialandlateraledgesofthisposterior interrelationships. In both trees IGM 100/
surface are abraded, as is the lateral surface 1309 is placed as the sister taxon of Aves,
of the lateral condyle. as part of the clade Ichthyornis (cid:49) Aves.
‹
tubercle; exg, extensor groove; fg, fibular groove; icg, intercondylar groove; ims, intermuscular scar;
lah, lig. acrocoracohumerale attachment (‘‘transverse groove’’); lc, lateral condyle; lcm, lateral cnemial
crest;mc,medialcondyle;ptf1,pneumotricipitalfossa1;ptf2,pneumotricipitalfossa2;s,tuberculated
scar; stc, articular surface for tibial cartilage; tre, extensor retinaculum tubercle.
6 AMERICAN MUSEUM NOVITATES NO. 3447
Fig. 3. Cladogram indicating the placement of the three new Mongolian specimens. The strictcon-
sensus cladogram of 316 most parsimonious trees (392 steps in length), from analysis of the dataset of
Clarke and Norell (2002) scored for the new material (see appendix 1), placed all specimens as part of
the clade Ornithurae.
When the proximal tibia(IGM100/1310;for 2002). Presbyornithid anseriforms and the
which only one character could be scored) putative ‘transitional shorebird’ form family
was included, 28 MPTs resulted (392 steps ‘‘Graculavidae’’, which have been reported
in length), a strict consensus of which yield- from the Nemegt Formation (Kurochkin,
ed the same topology as the analysis includ- 2000; Kurochkin et al., 2002), also lack this
ing allthreeelements.Finally,whenonlythe pneumatic foramen in the humerus. Howev-
distal tibiotarsus (IGM 100/1311) was in- er, there are problems in interpreting this
cluded, 18 MPTs (392 steps in length) re- character as indicative of presbyornithid or
sulted. A strict consensus of these trees ‘‘graculavid’’ affinities. As previously men-
placed IGM 100/1311 in a polytomy includ- tioned, a pneumatic foramen is ancestrally
ing Hesperornithesplusalltaxamoreclosely
lacking in Ornithurae (and Avialae; e.g.,
related to Aves than Apsaravis ukhaana.
Clarke, 2002; Clarke and Norell, 2002). On
the available evidence, therefore, the lack of
DISCUSSION
a pneumatic foramen could as easily be ple-
The proximal humerus (IGM 100/1309) is siomorphically retained as apomorphically
placed outside crown clade Aves by the lack acquired.
of a penetrating pneumatic foramen. This The well-developed fossa excavating the
foremen, although absent in a variety of taxa base of the humeral head in IGM 100/1309
nested within Aves (e.g., Ericson, 1997), op- is present in a variety of basal avian taxa
timizes as ancestrally present for the crown (e.g., fossil and extant galliforms) as well as
clade (Clarke and Norell, 2002; Clarke, in extant Charadriiformes (Baumel and Wit-
2004 CLARKE AND NORELL: NEW AVIALAN FOSSILS FROM MONGOLIA 7
mer, 1993), Passeriformes (Bock, 1962), and as the sister taxon of the clade Apsaravis
Procellariformes (Hope, 1999). This fossa ukhaana (cid:49) Aves. This placement would
has been used simultaneously as evidence to make it potentially outside of a clade known
supportreferraltoPresbyornithidae(Ericson, to have a pygostyle homologous with that of
2000), to the form family ‘‘Graculavidae’’ Aves (see pygostyle definition, and apomor-
(e.g., Olson and Parris, 1987; Hope, 1999), phy-based definition of ‘‘Ornithurae’’ in
to Charadriiformes, and as an example of Gauthier and deQuieroz,2001).However,in
mosaicism uniting these taxa (e.g., Hope, new analyses (Clarke et al., 2002; in prep.)
1999). As has been repeatedly remarked including two taxa placed as basal to Apsa-
(e.g., Clarke, 2000; Livezey, 2003), using ravis (Zhou and Zhang, 2001), a pygostyle
characterslikethisfossa(ofteninsmallnum- is present (Zhou and Zhang, 2001) and two
bers), whose distributions have not been op- cnemial crests are apparently lacking. Based
timized in analysis with appropriate taxon on these data, IGM 100/1310 is unambigu-
sampling, must result in correspondingly ously part of Ornithurae (sensu Gauthierand
weak systematic hypotheses. More inclusive de Quieroz, 2001).
analyses of basal avian relationships, includ- The distal tibiotarsus (IGM 100/1311) is
ing further well-represented fossil taxa and, placed outside of Aves by the absence of an
specifically, better preserved exemplars of ossified supratendinal bridge,whichoptimiz-
the taxon known from IGM 100/1309, are esasancestrallypresentinAves(e.g.,Clarke
necessary to more completely resolve its and Norell, 2002; Clarke, 2002). Isolated el-
phylogenetic placement. However, its cur- ements identified as part of Hesperornithes
rent, relatively unresolved placementbestre- from the Nemegt Formation include a distal
flects the most strongly supported phyloge- portion of a tibiotarsus also from Tsagaan
netic hypothesis given the data currently Khushu(Kurochkin,2000;seealsoIntroduc-
available. The specimen is easily differenti- tion). This specimen was identified as Bap-
ated from both the early CretaceousAmbior- tornis sp. (Kurochkin, 1988) and later re-
tus dementjevi (Kurochkin, 1985) and Apsa- identified as ‘‘more closely related to Para-
ravis ukhaana (Norell and Clarke, 2001; hesperornis’’ (Kurochkin, 2000: 545). This
Clarke and Norell, 2002), the twomostcom- distal tibiotarsus is nearly identical in mor-
plete avialans known from the Mesozoic of phology to IGM 100/1311. It is also close in
Mongolia,bythepresenceofthedistinctfos- size. Its distal mediolateral width is given as
sa excavating the posterodistal humeral head 11.7 mm (Kurochkin, 2000), compared to
as well as by comparison of nearly every 12.1 mm in IGM 100/1311. Both fossils are
other morphology of the proximal humerus. from individuals slightly more than one-half
Phylogenetic analysis of the proximal ti- the size of Baptornis advenus (e.g., AMNH
biotarsus IGM 100/1310 does not resolve 5101; 19.0 mm), the only named species of
whether it is a part of Aves. Relatively low Baptornis (Marsh, 1880; Martin and Tate,
cnemialcrestsinIGM100/1310(eventaking 1976).
into account abrasion) are present, for ex- Thesetwonearlyidenticalspecimensfrom
ample, in both Ichthyornis and some crown Tsaagan Khushu also share anteroposterior
cladelineages(e.g.,Tinamidae,Galliformes). compression, a broad extensor groove, as
These crests are, in contrast, comparatively well as a prominent fibular groove. These
high in Hesperornithes (Marsh,1880;Martin morphologies are present in Baptornis ad-
and Tate, 1976; Galton and Martin, 2002) venus(AMNH5101).Theproposedaffinities
and Presbyornithidae (Ericson, 2000) aswell of the tibiotarsus described by Kurochkin
as in other crown lineages (e.g., Anatidae, (2000) as closer to Parahesperornis than to
Charadriiformes). Baptorniswassupportedby‘‘fewdifferences
Relative to the other taxa included in the between the lateral and medial condyles, no
present phylogenetic analyses, it would be distal projection of the medial condyle and
ambiguous whether IGM 100/1310 was part the remarkable medial position of the exten-
of Ornithurae. The only character scorable sor groove’’ (Kurochkin, 2000: 545). These
from the fossil is missing data in Apsaravis differences from Baptornis advenus could
ukhaana, and the fossil could thus be placed not be confirmed. Instead, the extensor
8 AMERICAN MUSEUM NOVITATES NO. 3447
groove on IGM 100/1311 and the specimen sampled, and Hesperornithes are, indeed, a
commented on by Kurochkin (2000) appear cosmopolitan clade dominating inland river-
to have an extensor groove slightly morelat- ineandmarineenvironmentsintheLateCre-
erally located than in Baptornis advenus taceous of North America and Asia (Nessov,
(AMNH 5101; contra Kurochkin, 2000). 1992; Kurochkin, 2000).
The relevancy of emphasizing compari-
sons made to Hesperornithesisquestionable, REAPPRAISAL OF AVIALAN
however. It depends on how optimistic one DIVERSITY IN THE NEMEGT
is that the morphologies described from the FORMATION
distal tibia will be supported in analysis as
synapomorphies of Hesperornithes and/or a Both ornithurine and enantiornithine birds
subclade thereof. A well-sampled phylogeny are known from the Nemegt and Djadokhta/
with these characters optimized is lacking, Barun Goyot Formations, although ornithu-
and several characters are already known to rine remains have been more commonly re-
have a homoplastic distribution (e.g., Martin ported from the Nemegt (table 2). After the
and Tate, 1976), apparently associated with isolatedtarsometatarsusfromtheBarunGoy-
a diving habitus. For instance, anteroposte- ot Formation (Kurochkin, 2000) was re-
riorcompressionofthedistaltibiotarsalshaft moved from the Presbyornithidae (Kuro-
is seen in a variety of diving crown clade chkin et al., 2002) to Avialae incertae sedis,
taxa including phalacrocoracids, anhingas, no species or higher taxa less inclusive than
and some sphenisciforms (Simpson, 1946). Ornithurae and Enantiornithes are known in
Further, the compact bone layer in IGM100/ both the Djadokhta/Barun Goyot Formation
1311 (or IGM 100/1310 for that matter) is and the Nemegt Formation. Previous taxo-
not conspicuously thickened in comparison nomicassessmentoftheNemegtornithurines
to the condition in Baptornis advenus (Kurochkin, 2000) is consistent with Jerzyk-
(AMNH 5101) or Heperornis regalis iewicz and Russell’s (1991) conclusion that
(Marsh, 1880). the fauna from the Nemegt Formation is
Tibia IGM 100/1311 from Tsaagan Khu- more similar to North American Late Cre-
shuissimilartoBaptornisadvenus;however, taceous faunas than to Djadokhta/Barun
because these similarities are either shared Goyot faunas, as Presbyornithidae, ‘‘Gracu-
with other diving taxa, have an inadequately lavidae’’, and Hesperornithes are taxa which
investigated distribution, orareplesiomorph- have been proposed to have cosmopolitan
ic for Ornithurae, referral to this taxon is distributions and are known from the Late
weak at best. We conclude simply that IGM Cretaceous and/or Early Tertiary or North
100/1311 and the other distal tibia (Kuro- America (e.g., Ericson, 2000; Marsh, 1880;
chkin,1988,2000)fromTsaaganKhushuare Hope, 2002).
non-crown clade ornithurines incertae sedis. The kind of evidentiary support for the
Nessov (1992) suggested the presence of taxonomic assignments of previously de-
a small, possibly flighted, hesperornithine in scribed avialan material from the Nemegt
the Late Cretaceous of Central Asia, and an varies markedly. The large enantiornithine
array of other fragmentary material from from Gurilyn Tsav, Gurilynia nessovi (Ku-
across Central Asia has been referred to taxa rochkin, 1999), is known from a proximal
of Hesperornithes (Nessov and Prizemlin, humerus and proximal coracoid, and bothel-
1991; Nessov and Yarkov, 1993; Kurochkin, ements preserve optimized autapomorphies
2000). The referral of this material, and the of Enantiornithes (Kurochkin, 2000; i.e., V-
assumption that all non-crown cladeornithu- shaped humeral head and raised convex sur-
rines with diving modifications are part of a face for scapular articulation on the coracoid
monophyletic Hesperornithes, deserves re- [Chiappe, 1996]). However, the referral of
appraisalandis,forthereasonsstatedabove, partial, isolated cervical and thoracic verte-
problematic. If, however, futureanalysesand brae,atarsometatarsus,andadentulousman-
new discoveries support this conclusion, it dible to Hesperornithes (Kurochkin, 2000),
wouldimplythatLateCretaceousornithurine as well as the distal tibiae discussed here,
diversity is low, has been remarkably well rests on the more tenuous ground that there
2004 CLARKE AND NORELL: NEW AVIALAN FOSSILS FROM MONGOLIA 9
TABLE2
ComparisonofAvialanRemainsfromtheNemegtandDjadokhta/BarunGoyotFormations
are characters in each of these fragmentary Mesozoic age; Kurochkin et al., 2002: 2).
specimens that will, once investigated, opti- Teviornis gobiensis is known from associat-
mize as synapomorphies of Hesperornithes ed, well-preserved wing elements. It was
or a subclade thereof. We suggest this ma- identified asan anseriformbasedonthe‘‘ab-
terial be currently considered Ornithurae in- sence of craniocaudal curvature of corpus of
certae sedis. carpometacarpus (os metacarpale minus) rel-
Teviornis gobiensis is the only described ative to os metacarpale majus’’ (Kurochkin
Nemegt specimen referred to the avian et al., 2002: 4), a character from Livezey
crown clade (Kurochkin et al., 2002; Pres- (1997).However,lackofabowedmetacarpal
byornithidae: Anseriformes). Because of this III is primitive for Avialae (e.g., Clarke and
proposed systematic position, Teviornis is Norell, 2002) and is also plesiomorphically
relevant to the debate concerning fossil evi- retained within Ornithurae. Not only is this
dence for Cretaceous avian divergences (al- morphology present in nonavianornithurines
though there appears to have been confusion (e.g., Ichthyornis; Marsh, 1880), a straight
initially surrounding theholotypespecimen’s metacarpus is present in basal parts of Gal-
10 AMERICAN MUSEUM NOVITATES NO. 3447
liformes (e.g., Paraortigoides messelensis, Luis Chiappe for helpful comments on the
placed as the sister taxon of Galliformes manuscript. Tom Stidham also provided use-
(Mayr, 2000) and Palaeognathae (e.g., Lith- ful information about anseriform morpholo-
ornis; Houde, 1988), two clades themselves gy and called our attention to aspects of the
placed as two of the deepest divergences structure of Hesperornithes long bones. The
within the avian crown. Therefore, although Frick Fund of the Section of Vertebrate Pa-
relative to the set of extant taxa studied by leontology, American Museum of Natural
Livezey (1997), the absence of a curved History, supported this work.
metacarpal III would be a synapomorphy of
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istal extension of the dorsal edge of the car-
Bock, W.J. 1962. The pneumatic fossa of the hu-
pal trochlea) has been included in any anal- merus in the Passeres. Auk 79: 425–443.
ysis (Ericson, 1997; and is also present in Chiappe, L.M. 1996. Late Cretaceous birds of
Anhimidae). Another of these suggested southern South America: anatomy and system-
presbyornithid autapomorphies, a small in- aticsofEnantiornithesandPatagopteryxdefer-
terosseus dorsalis canal (Ericson, 2000; Ku- rariisi. Mu¨nchner Geowissenschaftliche Ab-
rochkin et al., 2002), is also present, for ex- handlungen (A) 30: 203–244.
Chiappe, L.M., M.A. Norell, and J. Clark. 2001.
ample, in Psittaciformes, Charadriiformes
A new skull of Gobipteryx minuta (Aves: En-
(Stegmann,1978),and,withinAnseriformes,
antiornithes) from the Cretaceous of the Gobi
in taxa other than thePresbyornithidae(Stid-
Desert. American Museum Novitates 3346: 1–
ham, personal commun.). The optimization
35.
of this character has also not been investi- Clarke, J.A. 2000. Setting limits on phylogenetic
gated in any analyses (e.g., Ericson, 1997; inference from isolated elements. Vertebrata
Livezey, 1997). In addition, no synapomor- PalAsiatica 38(suppl.): 9–10.
phies of Aves, Neognathae or Galloanseres Clarke, J.A. 2002. The morphology and system-
are described for, or appear preserved in, the aticpositionofIchthyornisMarshandthephy-
holotypeofTeviornisgobiensistosupportits logenetic relationships of basal Ornithurae.
Ph.D. dissertation, Yale University, New Ha-
proposed position nested within Anserifor-
ven, CT, 532 pp.
mes.
Clarke, J.A., and M.A. Norell. 2002. The mor-
In sum, our knowledge of MongolianLate
phologyandphylogeneticpositionofApsaravis
Cretaceous avialans and the fauna of theNe-
ukhaana from the Late Cretaceous of Mongo-
megt Formation are augmented by recentde- lia. American Museum Novitates 3387: 1–46.
scriptive work and the finds described here. Clarke, J.A., Z. Zhou, and F. Zhang. 2002. An
However, new and better preserved material ornithurinefromtheEarlyCretaceousofChina.
will allow a more complete assessment of Journal of Vertebrate Paleontology 22: 45A.
their phylogenetic and biogeographic impli- Dashzeveg D., M.J. Novacek, M.A. Norell, J.M.
cations. Clark, L.M. Chiappe, A. Davidson, M.C. Mc-
Kenna, L. Dingus, C. Swisher, and A. Perle.
1995.Unusualpreservationinanewvertebrate
ACKNOWLEDGMENTS
assemblage from the Late Cretaceous of Mon-
golia. Nature 374: 446–449.
We thank Mick Ellison for photographing
Efremov, I.A., 1954. Palaeontological research in
thespecimensandforpreparingfigure2,Ev- theMongolianPeople’sRepublic:resultsofthe
geny Kurochkin for access to specimens and expeditions of 1946, 1948, and 1949. Trudy
discussion of Mongolian fossil birds, and Mongol’skoi Komissii AN SSSR 59: 3–32.